Polyvinyl acetal resin sheets containing triethyl citrate



Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE POLYVINYL ACETAL RES SHEETS CON- TAINING TRIETHYL CITRATE SBY No Drawing. Application February 4, 1938,

Serial No. 188,674

3 Claims. (01. 260-36) This invention relates to plastic compositions, and more particularly to compositions comprising a polyvinyl acetal resin and a conditioning agent.

One object of this invention is to produce compositions of matter which may be made into permanently transparent, strong, and flexible sheets or films of desired thinness which are substantially waterproof, are unaffected by ordinary photographic fluids and possess the desired properties of a support for sensitive photographic coatings. Another object ofour invention is to produce compositions of matter which can be made into sheets suitable for use in laminated, shatter-proof glass. Still another object is to produce compositions which can be rolled, extruded, molded or otherwise worked into relatively thick sheets and massive plastics. A further object is to producecompositions suitable for use in lacquers, artificial silk filaments, wrapping tissues and the like. inafter appear.

We have discovered that triethyl citrate is a useful conditioning agent for polyvinyl acetal resms. accepted sense of the term, increasing the flexibility and toughness of polyvinyl acetal resin films, sheets, or other objects or masses containing it, but when used in amounts of about 40 or more parts per 100 parts of certain of the polyvinyl acetal resins, namely the polyvinyl acetal resins in which a predominating proportion of v the acetal groups are butyraldehyde acetal groups,

it has an unusual and remarkable effect which we may call ,elasticizing. That is to say, a sheet of a polyvinyl butyraldehyde acetal resin containing about 40 or more parts of triethyl citrate per 100 parts of resin possesses the property which, in the rubber industry, is known as nerve: namely, the property of stretching to a considerable extent when-tension is exerted upon it, and returning to its original dimensions when the tension is released. This property renders such sheets, which we shall call rubbery sheets, particularly useful in the manufacture of shatter-proof glass.

For the manufacture of cast films or sheets, the polyvinyl acetal resin and triethyl citrate may be dissolved in a suitable solvent or solvent mixture, such, for instance, as acetone, methanol, acetone-methanol mixtures, ethylene chloridemethanol mixtures, etc., about 300 to 500 or more parts of the solvent or solvent mixture being used per 100 parts of the resin. From about 3 to 100 or more parts of triethyl citrate per 100 parts of Other objects will here- Not only does it serve as a plasticizer in the resin may be employed, depending upon the nature of the resin and the purpose for which the sheets are to be used. Suitable proportions of triethyl citrate for any resin and any purpose may be readily determined by experiment. For the manufacture of sheets suitable for photographic film base, from 3 to 25 parts of triethyl citrate per 100 parts of resin are suitable. The resin solution is cast as a sheet, the solvent evaporated, and the sheet stripped from the casting surface.

Sheets for use in laminated glass may be formed by casting, or may be made without the use of volatile solvent by extrusion, for example in the manner set forth in application Serial No. 147,934 of John S. Kimble and Ernest C. Blackard, filed June '12, 1937. For instance, 40 or more parts of triethyl citrate and 100 parts of a polyvinyl butyraldehyde acetal resin may be mixed in a suitable, jacketed mixer at a low temperature, for example C., and the mixture may then be worked on hot rolls, in the manner described in U. S. Patent 2,048,686 of F. R. Conklin, until complete homogenization has taken'place. The mass thus produced may then be extruded through an annular die, and the tube so formed slit to form a sheet.

The polyvinyl acetal resins can be prepared by reacting polyvinyl alcohol with an aldehyde in the presence of an acetal condensation catalyst, e. g. a mineral acid. These resins can also be prepared by simultaneously de-esterifying a polyvinyl aliphatic ester and reacting the de-esterification product with an aldehyde in the presence of a de-esterifying catalyst and acetal condensation catalyst. Mineral acids are catalysts for both de-esterification and acetal formation. Among the polyvinyl acetal resins with which triethyl citrate is useful may be mentioned, as illustrative examples, the polyvinyl formaldehyde acetal resins, the polyvinyl acetaldehyde acetal resins, the polyvinyl formaldehyde acetaldehyde mixed acetal resins, the polyvinyl butyraldehyde acetal resins, and the polyvinyl butyraldehyde acetaldehyde mixed acetal resins.

Examples of the preparation of polyvinyl form'- aldehyde acetal resins may be found in U. S. Patent 1,955,068, Examples 1, 4 and 5; in U. S. Patent 2,030,092; Examples 1, 2, 3, 7 and 8; in British Patent 454,691, Examples 1, 2, 3, 4, 5, 6 and 7; in British Patent 404,279, Example 3; and in British Patent 436,072, Examples 1, 2, 3, 4, 5, 6 and 7.

Examples of the preparation of polyvinyl acetaldehyde acetal resins may be found in U. S. Patent 2,044,730, Example 1; U. S. Pate t 1,955,068, Example 2; U. S. Patent 2,036,092, Examples 4, 5 and 6; British Patent 466,598, Exampies 1, 2, 3, 4 and 7; British Patent 404,279, Ex amples 1, 2, 4, 5, 6, 7 and 8; U. S. Patent 1,990,399; and French Patent 808,578, Examples 1, 2 and 3. An additional example of the preparation of a polyvinyl acetaldehyde acetal resin is as follows: 100 lbs. of polyvinyl acetate, the viscosity of whose molar solution in benzene was 45 centipoises, was dissolved in 300 lbs. of 95% ethyl alcohol. To this solution were added lbs. of paraldehyde and 25 lbs. of HCl. The reaction mixture was allowed to stand for 4 days at C., after which it was diluted with ethyl alcohol, and the resin precipitated by pouring into cold water, washed and dried. Analysis showed the resin to have an acetate group content equivalent to 2.1% by weight of polyvinyl acetate and a hydroxyl group content equivalent to 12.9% by weight of polyvinyl alcohol.

Examples of the preparation of polyvinyl formaldehyde acetaldehyde mixed acetal resins may be found in British Patent 430,136, Examples 1, 2, 3, 4, 5 and 6; British Patent 445,565, Example 2; British Patent 465,873, Examples 1, 2, 3, 4, 5 and 6; French Patent- 808,586, Examples 1, 2, 8, 4, 5, 6, 12, 13, 14, 15, 16, 17, 18 and 19.

Additional examples of the preparation of polyvinyl formaldehyde acetaldehyde mixed acetal resins-are given in the application of Ralph H. Talbot, Serial No. 85,960, filed June 18, 1936, as follows:

Example 1 solution was complete, 10 parts of sulfuric acid (sp. g. 1.84) in 10 parts of water were added, and the mixture stirred. The mixture was maintained at a temperature of 40 C. for 144 hours. The contents of the vessel were then diluted with about two and a half volumes .of acetone, and the mixture precipitated into water. The precipitated resin was washed free from impurities by repeated changes of cold water, and dried. The resin, when analyzed, gave a hydroxyl group content equivalent to about 6.4 per cent by weight ofpolyvinyl alcohol, an acetate group content equivalent to about 4.0 per cent by weight of polyvinyl acetate, a formaldehyde acetal group content equivalent to about 15.9 per cent by weight of polyvinyl formaldehyde acetal and an acetaldehyde acetal group content equivalent to about 73.9 per cent by weight of polyvinyl acetaldehyde acetal. The polyvinyl acetal portion of the resin was therefore made up of about 19.7 per cent by, moles of polyvinyl formaldehyde acetal and about 80.3 per cent by moles of polyvinyl acetaldehyde acetal. in acetone to an extent which permitted coating a film or sheet from the resin.

"Example 2 50 parts (.58 mol; as monomer) of polyvinyl acetate centipoises), parts of ethyl'a'l. cohol; 90 parts of ethyl acetate, 17 parts (.385 I, mol. as monomer) of paracetaldehyde;2.9 parts; 1; f'

(.098 mol. as monomer) of .paraformaldehyde, 5 parts of sulfuric acid and 5 parts of water were'treated as in Example 11c;- .61 119W The resin was soluble I well washed and dried resin gave upon analysis a hydroxyl group content equivalent to about 9.6% by weight of polyvinyl alcohol, an acetate group content equivalent to about 4.1% by weight of polyvinyl acetate, a formaldehyde acetal group content equivalent to about 13.9 per cent by weight of polyvinyl formaldehyde acetal, and an acetaldehyde acetal group content equivalent to about 69.9 per cent of polyvinyl acetaldehyde acetal. The polyvinyl acetal portion of the resin was therefore made up of about 18.5 per cent by moles of polyvinyl formaldehyde acetal and 81.5

per cent by moles of polyvinyl acetaldehyde.

acetal. The resin was soluble in acetone to an extent which permitted coating a film or sheet from the resin.

"Example 3 1300 parts (15.1 mol. as monomer) of a polyvinyl acetate (45 centipoises), 1700 parts of ethyl acetate, 2250 parts of ethyl alcohol (95%) and 48 parts (1.57 mol. as monomer) of paraformaldehyde (trioxymethylene) were placed in a vessel equipped with a reflux condenser and a means of agitation, and the contents brought to a temperature of about C. by means of steam heating. 182.25 parts of sulfuric acid (sp. g. 1.84) dissolved in 51.5 parts of water were added, and the whole was heated at about 70 C. for about five hours, agitating throughout. At this point, 266.4 parts (6.05 mol. as monomer) of paracetaldehyde were added and heating at about 70 C. with agitation was continued for a further period of twenty hours. The contents of the reaction vessel were neutralized with ammonium hydroxide and diluted with water precipitating the resin as a cake. The cake was cut into small pieces and repeatedly washed with hot water until the resin was free from solvents, salts and other impurities. The resin, upon analysis, showed a hydroxyl group content equivalent to about 10.1 per cent by weight of polyvinyl alcohol, an acetate group content equivalent to about 3.2 per cent by weight of polyvinyl acetate, the remainder of the weight of the resin being polyvinyl acetal. The polyvinyl acetal portion of the resin was made up of about per cent by moles of polyvinyl acetaldehyde acetal and about 20 per cent by moles of polyvinyl formaldehyde acetal. The resin was not quite soluble in acetone, but could be made to dissolve by admixing small amounts of other solvents, such as alcohols, with the acetone."

Examples of the preparation of polyvinyl butyraldehyde acetal resins may be found in U. S. Patent 2,044.730, Examples 2, 5 and 6; British Patent 466.598, Example 5; French Patent 813,303, Example 1; French Patent 813,514, Examples 1, 2, 3 and 4; and British Patent 459,878, Examples 1, 2, 5, 6, 7, 8, 9 and 10.

An additional example of the preparation of a polyvinyl butyraldehyde acetal resin is as follows:

23.6 lbs. of polyvinyl acetate, the viscosity of those molar" solution in benzene was 45 centipoises, was dissolved in 56.5 lbs. of ethyl alcohol. To this solution was added 7.9 lbs. of

I butyraldehyde'and 5.9 lbs. of 35% HCl. The re- ,action mixture was allowed to stand for 4 days at 405C *after which it was diluted with ethyl 'nd- -ac'etic acid, and the resin precipi- I, 'ouringinto cold water, washed, and I H showed "the resin to have an acetate group content equivalent to 3.1% by -weight-or P yvinyl acetate and a hydroxyl group content equivalent to 16.3% by Weight of poly- 2 A transparent, rubbery sheet comprising 100- vinyl alcohol. parts of a polyvinyl butyraldehyde acetal resin A example of the P of a polyvinyl and at least 40 parts, approximately, of triethyl butyraldehyde acetaldehyde mixed acetal resm citrate an elasticizer therefon 5 is given in French Patent 813,303 Example 2. 4 5

A transparent, rubbery sheet comprising a What we claim as our mventlon and desire to be secured by Letters Patent of the United States polyvmyl metal f m wmch aspredommatmg. I proportion of the acetal groups are butyralde- 1. A transparent, rubbery sheet comprising 100 h yde acetal groups, an amount of tnethyl 10 parts of a polyvinyl acetal resin in which a. prefiltrate m- 9 lmpart' to W 10. dominating proportiun the a etal groups are .bery Character wlthout Substantially lmpalring butyraldehyde acetal groups, and at least 40 155 transparency parts, approximately, of triethyl citrate as an ,HENRY SMITH; elasticizer therefor. DONALD R. SWAN. 

